1. Field of the Invention
The present invention relates to a recorded magnetization state measuring method and recorded magnetization state measuring device for analyzing the magnetization state of a magnetic recording medium (hereinbelow referred to as simply "medium") such as a magnetic tape or magnetic disk.
2. Description of the Related Art
In the prior art, the recorded magnetization state of a medium on which recording was effected by a recording head was evaluated by means of the reproduced signal by way of the reproducing head as shown in FIG. 1. In Step 111, a recorded magnetization pattern was first formed on the medium by a recording head. In Step 112, this recorded magnetization pattern was then reproduced by the reproducing head, and the output reproduction was measured. In Step 113, the S/N ratio (Signal-to-Noise ratio) of the medium was found based on this output reproduction.
In recent years, output has been improved due to the use of a magneto-resistance type reproducing head instead of the magnetic induced type head of the prior art. However, in areas within the medium having high recording density, the output is still low, and this prevents an accurate evaluation of the recorded magnetization state. In addition, this output is affected by the characteristics of the reproducing head, and the recorded magnetization state is therefore extremely difficult to accurately evaluate by means of the reproduced signals of the reproducing head.
Furthermore, high levels of recording density give rise to recording distortion in the magnetic recording medium. Recording distortion includes non-linear transition shift, partial erasure, and transition broadening. Non-linear transition shift is generally measured by 5-th harmonic method (as disclosed, for example, IEEE Transactions on Magnetism, Vol. 27, No. 6, 1991, pp. 5316-5318. (Y. Tang and C. Tsang))
In addition, it is clear that for a three-dimensional harmonic component V3 of a recording density D, and a fundamental harmonic wave component V1 of a recording density 3D, V1/(3.multidot.V3)=1 if partial erasure is not present, and V1/(3.multidot.V3)&lt;1 if partial erasure is present. Partial erasure can therefore be measured quantitatively by using this relation. This fact was reported at the 1996 Intermag International Conference (address number GP29).
Nevertheless, the prior art has the following problems:
(1) Problems of measurement by the reproducing head
The first problem resulting from measurement by the reproducing head is that evaluation of the recorded magnetization state is prevented in areas having high recording density. The chief reason for this difficulty is that, if the reproduction gap-length and minimum recording wavelength are nearly equal, output drops due to gap loss, thereby preventing accurate measurement of the recorded magnetization state. The gap-length of a reproducing head of the current art is on the order of 0.1-0.2 .mu.m, smaller gap-lengths being extremely difficult to achieve at the current state of the art. Even assuming the use of a reproducing head with smaller gap-length, output reproduction is also extremely difficult to estimate. A second reason for the above-described problem is that the output signal drops due to the effect of spacing during reproduction in high-density areas, thereby preventing the accurate measurement of the recorded magnetization state. If the effect of spacing can be eliminated, the recorded magnetization state can be accurately determined.
The second problem is that local recorded magnetization states of the medium cannot be accurately evaluated. The reproducing head cannot be reduced to a width of less than 1-2 .mu.m because a reproduction track that is too narrow does not produce sufficient output reproduction. When measurements are carried out by the reproducing head, local recorded magnetization state in areas smaller than the reproducing head cannot be measured, with the result that a local recorded magnetization state in a range smaller than 1 .mu.m within a track (for example, the recorded magnetization state at the edges of a track) cannot be accurately determined.
(2) Problems encountered in measurement of the amount of non-linear transition shift by the 5-th harmonic method
The problem encountered in measuring the amount of non-linear transition shift by the 5-th harmonic method is that non-linear transition shift cannot be measured in isolation. In other words, methods of the prior art produce a measurement of the combination of non-linear transition shift and partial erasure rather than an accurate value for the amount of non-linear transition shift alone.
(3) Problems encountered in measurement of partial erasure
The main problem encountered in measuring partial erasure is that prior-art measurement methods assume that the reproduced waveform is vertically symmetrical. In actuality, by the reproducing head in most cases a waveform is vertically asymmetrical and therefore the reproducing head in most cases does not meet this assumed condition, thereby giving rise to error.
A second problem is that the details of partial erasure cannot be understood in measurement methods of the prior art. Measurement methods of the prior art determine partial erasure by measuring the average phenomena of the overall track width of the reproducing head by means of the signal reproduced by the reproducing head. However, since adequate output reproduction cannot be obtained if the reproduction track-width is too narrow, the reproducing head width cannot be made less than about 1-2 .mu.m. As a result, the state of an area smaller than the reproducing head, i.e., a local state within a range smaller than 1 .mu.m within a track (for example, the state of a track edge) cannot be accurately determined.